This invention relates to precision location of electronic devices. More specifically, the invention relates to a method and apparatus for precision location of electronic devices, particularly indoor, via local broadcast signals.
Present techniques for locating electronic devices (e.g., cellular phone, PDA or computer, etc.) including indoor locations (such as shopping malls and office buildings) require either: 1) satellite (global positioning signals xe2x80x9cGPSxe2x80x9d) signals; or 2) GPS and assistance via cellular signals to penetrate building structures, when required; or 3) triangulation using the cellular system. The cell sites are designed to have limited coverage, so finding useful signals from more than two cell sites is unlikely when indoors.
Presently, two major approaches to GPS precision location dominate. The first, a mostly outdoor, satellite vehicle-based Global Positioning System that receives a feeble code division multiple access xe2x80x9cCDMA-likexe2x80x9d signal from several satellites in which a receiver (using complex search routines and hardware) determines its position via the delay calculated using the received GPS signal phase, the GPS almanac and ephermis. This procedure takes several minutes in weak signal environments. The second is a system that extends the above system through use of additional information supplied via a cellular wireless network.
Snaptrack has disclosed a xe2x80x98communicationxe2x80x99 system for providing GPS aiding information useful in the above second system (e.g., see U.S. Pat. Nos. 5,841,396 and 5,874,914). Communication systems require two-way signaling and information transfer. The concept is known as Assisted GPS. The SnapTrack implementation uses a communication system to send the GPS almanac, ephermis and transfer of time from the base station to the mobile. In one mode, intermediate results are returned to the base station (and network) for further processing. With these quantities (GPS hints), the correlating receiver knows what and when to look for the appropriate satellites and can add the successive correlations of several tens of measurements, effectively pulling the feeble buried signal out of the thermal noise.
The United States Government through the Federal Communications Commission xe2x80x9cFCCxe2x80x9d has mandated a gradual phase-in of location detection technology in cellular phones/systems for emergency 911 applications. Oct. 1, 2001 was the deadline for E911 phase II. In recent months, the Location Based Services Report (LBS Report)(http://pulver.com) has raised concerns that present technologies deployed for 911 would not provide adequate coverage in some indoor environments.
Today, most mobile 911 calls come from callers on the road in open environments where high location accuracy can be achieved. However, as personal communications shift from landline telephones to wireless devices in coming years, people will expect that their wireless appliances will provide them with emergency services at all locations including multi-story buildings, subway stations and similar structures. Sadly, the need for indoors tracking was clearly demonstrated during the tragic events of Sep. 11, 2001 at the New York World Trade Center.
Unfortunately, large steel and concrete buildings, subways and large malls may be difficult or even impossible to cover using traditional wide area location technologies such as AGPS (Assisted GPS) and TDOA (Time Difference of Arrival). Low signal to noise ratio and signal multipath effects in these environments decrease tracking accuracy or even prevent signal acquisition.
Multiple story buildings pose additional obstacles for tracking, as they require three-dimensional positioning. Even if the longitude and latitude of an individual in a fifty-story building were known with great accuracy, that knowledge would be insufficient because the emergency team may have to search every floor. For an accuracy of 200 meters, the location fix may cover many multi-story buildings. Under these conditions, a rescue team could spend hours just searching for the caller.
Many of the major wireless operators chose AGPS solution to meet the E911 Phase II requirements. This technology has several very attractive features. It does not require significant infrastructure changes, and in outdoor rural environments, it offers accuracy that is unsurpassed by any fielded technology. Nevertheless, in some urban settings AGPS may not be reasonably accurate due to multipath, reflected signals.
In evaluating its AGPS tests, Cingular Wireless (Aug. 31, 2001) commented to the FCC, xe2x80x9cAlthough the Snaptrack system (an AGPS solution) performed well in an outdoor environment, indoors test results were extremely poor, effectively negating the outdoor results. Indeed, indoor call yield were so low that meaningful comparison with the Commission""s accuracy standards could not be tabulated.xe2x80x9d
An article in the June 2001 pulver.com Location Based Services Report presented test results of the CoCoSecom AGPS/AFLT (Advanced Forward Link Trilateration) system in Osaka Japan. These results are consistent with Cingular Wireless observation that AGPS provides superior results for outdoor environments and inferior results in indoors settings. The results also indicate that the accuracy of the technology inside large buildings and underground structures would be insufficient to meet the needs of emergency services. It should be noted that CoCoSecom employs QUALCOMM""s MSM3300/gpsOne system, which will also be used by some of the US CDMA carriers for their E911 solution.
The issue of indoors tracking has also been addressed by the Coordination Group on Access to Location Information by Emergency Services (CGALIES), whose charter is to explore options for implementing E112 emergency services in the European Union. CGALIES (http://www.telematica.de/cgalies) Work Package1, released on Apr. 19, 2001 states, xe2x80x9cA general description of environments where AGPS is typically demonstrated to work well is: outdoors, in car, in wooden buildings, in two story buildings of brick/slate, and in steel/concrete buildings 1-3 meters from a window.xe2x80x9d
In addition to AGPS, other technologies such as TDOA and E-OTD (Enhanced Observed Time Difference of Arrival), have been adopted by some carriers.
The preceding discussion makes it quite clear that present technologies selected to meet the E911 Phase II requirements do not address the needs of providing emergency services in large buildings, subways and other difficult urban areas. In these areas, even greater accuracies than those mandated by the FCC are needed to reduce response time to 911 calls.
A location determination apparatus, method and system that is an improvement upon existing location determining techniques. The invention enables precision indoor location determination through the use of non-DTV terrestrial broadcast signals (e.g. one way, wide area, dissemination of information), or re-broadcast signals of the proposed (terrestrial based) digital satellite radio relay transmitters to provide position location. This solution does not require a local receiver to correct for long distance propagation dispersion, particularly for the satellite relay, as the digital radio satellites are already synchronized to GPS time. More specifically, the invention discloses two significant location detection concepts: A) local terrestrial transmitters provide information used to determine the location of an electronic apparatus; and B) local re-transmitters of satellite-distributed programming provide information used to determine the location of an electronic apparatus. Within each of concepts A and B, there are three methods of calculating location position: 1) the handset in a standalone mode measures the time difference of arrival from three or more synchronized transmitters; the handset has a lookup table of the transmitter locations and uses that information to compute latitude and longitude; 2) the handset in an assisted mode receives LMU (local monitoring unit) timing errors of the local transmitters and uses that information along with the previously acquired transmitter locations to calculate latitude and longitude; and 3) the handset in a server based mode receives calculated position information from a server which had received LMU data and local transmitter location and the handset time difference of arrival information.